1. Field of the Invention
The present invention relates to an optical isolator and, in one application, to an optical fiber feedthrough assembly having an isolator therein.
2. Description of the Prior Art
An isolator is an optical device operative to permit passage of light in one direction but to prevent the passage of light in the opposed direction. The central component of an isolator is a material, typically a crystalline material, which is capable of rotating the plane of polarization of light passing through in response to the application of an external field, typically a magnetic field. On each facial surface of the crystal is provided a polarizer. Each polarizer has a different plane of polarization associated with it.
Early optical isolator technology used a ferromagnetic rare earth garnet material such a yttrium iron garnet material. Presently, however, the material of choice for an isolator is an epitaxially grown bismuth iron garnet ("BiG") material. Isolator technology is discussed in Electronic Times, 21 Nov. 1991.
Light is coupled into and from the polarizer surfaces of the isolator using a lens. U.S. Pat. No. 4,701,011 (Emkey et al.) discloses an arrangement whereby a graded index optical fiber may be mounted to the end of a single mode fiber to serve as a lens.
Presently available opto-electronic apparatus utilize active opto-electronic devices, such as solid state lasers or diodes. The active opto-electronic device is mounted within a suitable sealed housing. Light impulses emitted from or directed onto lasers or diodes, respectively, are carried between linked transmitters, receivers, or other opto-electronic apparatus on optical fiber links. The passage of the optical fiber into the respective housing of the opto-electronic apparatus is facilitated using a structure known as a feedthrough assembly. The housing and feedthrough provide a degree of environmental isolation between the inside and outside of the housing. Representative opto-electronic apparatus and/or feedthrough assemblies are disclosed in U.S. Pat. No. 4,119,363 (Camlibel), U.S. Pat. No. 4,615,031 (Eales), U.S. application Ser. No. 07/453,831, filed Dec. 19, 1989 (now abandoned), U.S. Pat. No. 5,177,806, U.S. Pat. No. 4,826,276, U.S. Pat. No. 4,865,410, and U.S. application Ser. No. 07/725,777, filed Jun. 17, 1991 (now abandoned).
It is known to use an isolator to prevent back reflections of light from affecting active opto-electronic components. However, the relatively large size of presently available isolators and, owing to the high material cost, their relatively high expense (on the order of $2000) are perceived disadvantages attendant with their use.
In view of the foregoing it is believed advantageous to provide a miniature isolator, and in particular, an isolator element sized for receipt within a feedthrough assembly.